The field of the invention relates to a vehicular speed control system having reduced audible gear chatter.
A typical speed control system includes a DC motor coupled to an engine throttle by mechanical transfer gears. The DC motor is usually responsive to a feedback loop which compares actual vehicle speed with a set or desired speed to generate an error signal. Accordingly, the engine throttle is rotated by the DC motor in a direction to reduce the error signal. Since the inertia load (transfer gears, throttle linkage, and throttle) does not abruptly change, and the DC motor rotates at substantially constant velocity, gear chatter has not been a problem with these systems. Stated another way, backlash between mating transfer gears has not been recognized as a problem with conventional speed control systems.
The inventors herein have recognized, and appear to be the first to have recognized, that gear backlash may be a problem when certain stepper motors are employed in speed control systems. More specifically, when the stepper motor rotates in discrete phase steps, the resulting nonconstant angular velocity may result in a transfer gear backlash. This backlash may result in audible gear chatter which the vehicular operator may find disturbing. The inventors herein have also recognized that anti-backlash gears may be utilized to advantage in a speed control system employing a stepper motor which rotates at nonconstant angular velocity. However, the inventors herein believe that conventional anti-backlash gears are not suited for assembly in a mass production environment. More specifically, prior anti-backlash gears required complicated assembly of springs, pins, split gears, and retaining rings which require considerable manual dexterity and therefore results in time consuming assembly operations.